EP2091663B1 - Ultrasound liquid atomiser - Google Patents

Description

Field of the invention

The present invention relates to fluid dispensers, commonly called atomizers, which make it possible to accurately diffuse, by means of piezoelectric elements, fluids in the form of micro droplets or aerosols.

State of the art

The distribution of fluids or liquids, whatever their nature (oily, aqueous or alcoholic), whether solutions or suspensions (particles suspended in a liquid), is carried out in a large number of applications by micronisation, atomization, nebulization or aerosol generation. The main applications using these fluid delivery devices concern the administration of drugs (pharmacy), the diffusion of cosmetic products (in particular perfumes), disinfection, odor generation, humidification of the air or supports (paper, textiles ...) and the distribution of biological reagents.

In medical applications, nebulizers have been used for decades to deliver drugs by inhalation. The devices used for this purpose may comprise a mechanical metering pump, a pneumatic or ultrasonic nebulizer. Until recently, these devices were intended to deliver drugs through the respiratory tract, at a relatively superficial level. In recent years, the pharmaceutical industry has been interested in administering drugs in the form of aerosols in the deep lungs to reach the bronchioles. In doing so, it would become possible to administer systemic drugs or genes by respiratory route.

To do this, it is necessary to develop new technologies to improve the yield, accuracy and homogeneity of aerosols intended to be deposited in the bronchioles. The traditional devices are, in general, limited either by a too high speed of expulsion of the aerosol, or by too much consumption, or by a degradation of the drug products, or by a too large droplet size, or by the noise.

To meet the new requirements of respiratory drug delivery, several aerosol generator manufacturers have developed devices based on grids or vibrating micro-perforated membranes. These manufacturers include Nektar (Aeroneb), Odem (TouchSpray), Pari (e-Flow), Pfeiffer (MicroHaler), Omron (NE-UO22), Sheffield Pharmaceutical (Premaire), Alexza (Staccato).

The first studies of ultrasonic atomizers with a vibrating micro-perforated membrane were performed by the Matsushita research laboratory in the 1980s. The principle of the ejection of liquid into fine droplets through a vibrating micro-perforated vibrating membrane is particularly developed in the following publications: Ueha S., et al. Mechanism of ultrasonic atomization using a multi-pinhole plate. Acoust.Soc. Jpn. (E) 6.1: 21 (1985). Maehara N., et al. Influence of the vibrating system of a multipinhole-plate ultrasonic nebulizer on its performance. Review of scientific instruments, 57 (11), Nov. 1986, pp.2870-2876 . Maehara N., et al. A pinhole-plate ultrasonic atomizer. Ultrasonics Nov. 1984 .

All of these studies have been the subject of several patents, in particular US 4,533,082 (1985) ) and US 4,605,167 (1986) ) which describe an atomizer using a vibrating membrane perforated with micro holes. The membrane has a curved portion (protuberance or dome) at its center to diverge the generated droplets. The membrane has micro-perforations 30 to 100 microns in diameter. The vibrating element is an annular piezoelectric ceramic with an outside diameter of 5 to 15 mm and an inside diameter of 2 to 8 mm. The vibrating membrane with a thickness of 30 to 120 μm is bonded to the annular ceramic. This piezoelectric ceramic is excited at frequencies between 30 and 200 kHz in its mode of radial deformation. The Bespack patent US 5,152,456 (1992) ), see also the corresponding European application, EP 0 432 992 A1 , in accordance with the preamble of claim 1, reproduces the principle proposed by Matsushita. However, the vibrating element (or vibrator) consists of an aluminum annular disk of 22 mm in diameter. The piezoelectric ceramic is fixed on this aluminum disk. The operating mode of the piezoelectric ceramic corresponds to a radial deformation. The central opening of the aluminum disc is 4 mm. The nickel membrane has 1500 perforations (or holes) of 3 μm in diameter.

The Toda patent US 5,297,734 (1994) ) refers to a vibrating blade atomizer of square geometry allowing flow rates up to 1 l / hour. The atomizer consists of a 50 μm thick nickel membrane bonded to a piezoelectric ceramic disk with an outside diameter of 24 mm, an internal diameter of 12 mm and a thickness of 6 mm. The diaphragm has tapered holes with inner diameter 1 mm and outer diameter 20 μm.

The Technology Transfer Partnership (TTP) Patent US 5,261,601 (1993) ) discloses an atomizer based on the aforementioned Bespack patent. The TTP patent US 5,518,179 (1996) ) refers to a disk atomizer or the perforated membrane is electro-formed nickel. The TTP atomizer does not require a liquid chamber behind the membrane and the liquid supply is carried out by capillarity (use of wick or porous material). The atomizer TTP highlights its bimorph structure specifying the bending mode of the assembly consisting of the piezoelectric ceramic and the micro-perforated membrane. The membrane is of comparable rigidity to that of the annular piezoelectric ceramic. The reference atomizer consists of a brass ring with an outside diameter of 20 mm and a thickness of 200 μm. The piezoelectric ceramic ring has an outer diameter of 20 mm, an inside diameter of 6 mm and a thickness of 200 μm. The patent US 6,085,740 (2000) ) of Aerogen mentions a means for atomizing a liquid into fine droplets using a micro-grid. The membrane, provided with micro-holes 1 to 6 μm in diameter, is vibrated by a piezoelectric bimetallic operating at 45 kHz. The liquid is supplied by capillarity and the membrane is separable from the vibrator.

The patent US 6,427,682 (2002) to Aerogen describes the realization of a drug diffusion apparatus using a vibrating membrane. Its principle is very close to that of Matsushita. It consists of an aluminum part vibrated by bending using an annular piezoelectric ceramic. The vibrating membrane provided with micro-holes is made by electroforming. A chamber containing the liquid is in contact with the membrane.

In addition, Omron has developed an ultrasonic pump technology for atomizing a liquid through a micro-perforated membrane. This technology is described in the patent US 6,901,926 (2005) ). In Omron technology, the micro-perforated membrane is not directly vibrated by the vibrating element. The droplets are formed by ejecting the liquid through the holes during dynamic pressure variation due to the ultrasonic pump.

The piezoelectric or ultrasonic atomizers of the state of the art (frequency greater than 20 kHz) which comprise a micro-perforated membrane subjected to vibration all function by bending the membrane and the piezoelectric ceramic associated therewith. It is in fact to combine in different ways an annular piezoelectric ceramic and a thin metal membrane having a large number of micro perforations. This type of structure has a small thickness.

The devices of the state of the art, however, have several disadvantages.

A first disadvantage lies in the fact that the micro-perforated membrane strongly participates in the resonance mode of the atomizer. This phenomenon has the effect that the atomizer is itself strongly damped in its resonance by the liquid that is in contact with the membrane. The operation of the atomizer is highly dependent on the amount of liquid or the pressure exerted by the liquid behind the membrane. This results in a complication in controlling the excitation frequency of the atomizer. In addition, this damping leads to a heating of the vibrating element and the membrane. This heating has the effect of limiting the operating time of the atomizer, to increase the power consumption necessary for the operation thereof and may lead to a degradation of the properties of the liquid to be atomized. Moreover, in this type of structure, the deformation of the bending membrane does not allow to obtain a homogeneous displacement over the entire surface of the membrane. Depending on the location of the micro-holes on the membrane, they do not have the same flow and the generation of aerosol can be unstable (threshold effect). On the other hand, the sensitivity of the vibrating structure to mechanical fasteners and liquid seals (parasitic damping) make complex and costly the technological solutions for industrially implementing such structures in large quantities and at low cost.

There is therefore a need to overcome these disadvantages and to provide more robust devices, easier to control electronically, more energy efficient, easier to industrialize in large quantities and low cost.

General description of the invention

The present invention proposes to remedy in particular the problems described in the previous chapter.

For this purpose, it relates to an atomizer as defined in the main claim.

Preferred embodiments are the subject of the dependent claims.

In the present text, "transducer" means an element consisting of a piezoelectric transducer body, at least one piezoelectric element and optionally a rear mass.

By "section" is meant a geometrical figure formed by the intersection of a plane and a volume. Thus, considering for example a cylindrical object whose interior has a variable diameter, it will say that it has a variable section over its length.

The transducer body has an axis of symmetry.

Several advantages offered by the atomizer according to the present invention result from the fact that the piezoelectric transducer body on which is fixed the membrane vibrates in a longitudinal mode, that is to say, in a direction parallel to the axis of symmetry of the body of the piezoelectric transducer.

One or more piezoelectric elements may be provided.

Preferably, the section of the piezoelectric transducer body varies along its length.

According to one embodiment, the section varies discontinuously.

Advantageously, the section varies abruptly in one place.

Such sectional variation is illustrated in the following embodiment in which the piezoelectric transducer body has two parts whose outer diameter differs. The zone of amplification of deformations whose end comprises the membrane has the smallest diameter. In this configuration, called "trompe" in this text, the ultrasonic waves longitudinal are amplified in displacement during the change of section of the transducer. The tubular element acts as an amplifier for longitudinal micron displacements.

According to another embodiment of the invention, the membrane at least partially forms a dome that performs several functions. In common with the state of the prior art, the micro-perforated membrane is designed to retain the liquid in the atomization chamber at the rear of the membrane and to contain the static pressure thereof. The pressure balance, the shape of the holes and the nature of the material used for the membrane is so that the liquid does not ooze outside the membrane and no phenomenon of "dripping" or loss of liquid n appears. In addition, the dome shape makes it possible to better distribute the mist of micro-droplets or aerosol by causing the jet to diverge by a simple geometric effect. On the other hand, the vibratory speed associated with the displacement of the membrane makes it possible to eject the micro-droplets through the holes. In the case of the present invention, the dimensions of the dome and the micro-perforated membrane are such that the dome plays a vibratory motion amplification effect while maintaining a homogeneous vibration velocity distribution on the surface of the membrane. Unlike the state of the prior art, the membrane does not influence the vibratory behavior of the transducer. Whatever the thickness of the membrane (for example from 20 to 200 μm), the piezoelectric element retains its dynamic characteristics and its vibratory performance. More specifically, the resonant frequency and the vibratory displacements of the transducer are not modified by the mechanical coupling of the membrane. This provides advantages to the atomizer in that the transducer design (frequencies, vibratory displacements, deformation modes, coupling coefficient and mechanical quality factor) can be performed without regard to the membrane (geometry and material).

This property of the present invention advantageously makes it possible to optimize the structure of the transducer (or converter) in order to favor either the exit speed of the aerosol, the flow rate, the resonance frequency, the consumption or the efficiency of the transducer. . In this way, it is possible to produce vibrating membrane atomizers for the production of aerosols at almost zero speed (medical application) up to ejection speeds for example of the order of 30 m / s (cosmetic application ). Similarly, the atomization rate is no longer directly related to the surface of the piezoelectric ceramic but to the length of the piezoelectric transducer for adapting flow rates of 1 .mu.l / s to 300 .mu.l / s. It is this same length that directly governs the resonance frequency of the atomizer. The operating mode of the atomizer is not a bending mode but a mode of longitudinal elongation. This makes it possible to work at high frequencies (50 to 200 kHz) with piezoelectric ceramics of small diameter without penalizing the flow of liquid and especially with very low losses. These mechanical losses that correspond to an energy dissipated to heat in the transducer rise sharply depending on the operating frequency of the transducer. In the present invention, these are reduced because the yields of the longitudinal transducer type structures are much better than the "bimetallic" type structures operating in flexion.

The low losses in the transducer lead to the design of atomizers whose power consumption is low. This advantage is considerable insofar as the atomizers of the state of the prior art are limited in their application by the duration of atomization and the service life of the batteries or supply batteries. Indeed, the advantageous applications of vibrating micro-perforated membrane atomizers essentially concern "hand-held" devices operating on batteries or batteries. The structure, object of the present invention, is less damped by the liquid behind the membrane. This property allows less heating of the liquid to be atomized. In applications or atomizers deliver drug formulations, a heating of the liquid can be unacceptable and greatly limit the interest of such atomizers.

Furthermore, according to a preferred embodiment, the present invention is characterized in that the vibration nodes are accessible to easily allow the mechanical attachment of the atomizer. The atomizers of the state of the art operating by bending the annular ceramic are difficult to mechanically fix without disturbing and strongly damping the vibration mode. In the case of the present invention, the atomizer is preferably mechanically fixed or overmoulded in the area of the vibration node (this node is unique) and allows very simple and very inexpensive mechanical mounting and sealing solutions.

Another feature of the invention is that the liquid can be directly brought into contact with the rear face of the membrane. Indeed, the mode of vibration of the atomizer in a longitudinal mode is insensitive to the presence of a liquid and the weight of the column of this liquid.

This property allows the atomizer to operate indifferently at an angle that can vary from vertical to horizontal.

The liquid can also be guided to the membrane by capillarity using suitable channels, wicks or porous materials. In this way, the liquid reservoir may be above, around or below the atomizer.

According to a variant of the invention, the structure of the atomizer comprises a rear mass, also called dynamic mass, whose role is to prevent the transducer from vibrating at the back, two piezoelectric ceramics connected by a common connectivity, a vibratory motion amplifier comprising a cavity and a micro-perforated membrane of varied shape but preferably convex forming a protuberance or dome.

According to another variant of the invention, a preloading mechanism such as a screw makes it possible to mechanically link the rear mass, the ceramics and the amplifier. The amplifier is metallic and preferably in stainless steel, titanium or aluminum. The micro-perforated membrane is stuck on the vibratory amplifier. The membrane, which has little influence on the vibratory behavior of the atomizer, can be made of various materials such as plastic, silicon, ceramic but is preferably made of metal. The micro-perforations can be made by various means but preferably by electroforming or by laser. The amount of micro-perforations can range from one hole for liquid distribution to demand, to several thousand holes. The size of the micro-holes or mesh of the grids can range from 1 μm to 100 μm in equivalent diameter depending on the applications of the atomizer. It has been demonstrated that the performance in flow and homogeneity of the jet of droplets of the atomizer were highly dependent on the mode of displacement of the membrane. These performances are improved if the diaphragm moves in "piston" mode without bending deformation. In the state of the art, the atomizers operate in bending and thus lead to one or more vibration nodes inside the membrane. In the present invention, the membrane does not participate in the vibration mode of the transducer and it is possible to size and optimize the geometry of the membrane so that it deforms in "piston" mode. For this purpose, the modelizations and the test results show that the diameter of the protuberance (or dome) must be close to the diameter of the cavity containing the liquid (or chamber). This implies that the maximum height of the dome must be close to half the inside diameter of the cavity.

The displacement of the membrane in "piston" mode makes it possible to homogenize the vibratory speed on the surface of the membrane. As a result, micro-perforations (or holes) eject micro-droplets of better calibrated sizes and with an identical flow rate when compared to each other.

• Le ou les éléments piézoélectriques sont représentés par une seule céramique fixée avec une colle de rigidité suffisante sur le transducteur soumis à mouvement vibratoire.
• La céramique piézoélectrique est un multicouche permettant une alimentation électrique de faible tension (1 à 15 V_DC) comme peuvent en fournir, par exemple les sociétés Epcos, Fuji, Noliac, Morgan Matroc ou Physic Instruments.
• La céramique piézoélectrique est fixée sur le corps du transducteur de telle manière qu'il n'y ait aucun contact entre celle-ci et le liquide à atomiser. Cette configuration permet d'isoler électriquement la céramique piézoélectrique et élimine tout problème d'étanchéité et de compatibilité (application médicale) avec le liquide.
• L'amplificateur de déplacement vibratoire (ou « trompe ») de l'atomiseur comporte des passages, rainures ou trous de telle manière que la chambre ou le réservoir de liquide est situé autour de la trompe.
• Le transducteur piézoélectrique de l'atomiseur comporte un « pavillon » à l'extrémité de la «trompe» qui vibre préférentiellement suivant un mode « piston » sans aucune flexion. Ce « pavillon » a l'avantage d'amplifier le déplacement vibratoire du transducteur mais aussi de pouvoir fixer une membrane micro-perforée de plus grand diamètre. Cette configuration est destinée à augmenter le débit de l'atomiseur malgré sa petite dimension.
• Le transducteur piézoélectrique, fonctionnant en mode longitudinal, fait vibrer et se déformer une membrane micro-perforée ou une grille de forme cylindrique. Pour optimiser le déplacement de la membrane cylindrique qui est placée entre le transducteur et le pavillon, une protubérance peut être ajoutée afin de rigidifier la membrane de manière adéquate.
• L'atomiseur comporte une « trompe » de forme particulière comme, par exemple, un tronc de cône permettant une amplification de mouvement vibratoire par changement brutal de section. Dans cette configuration particulière, le ratio de la distance membrane-élément piézoélectrique sur le diamètre de l'élément piézoélectrique est de préférence supérieur à 0,5.
• La membrane micro-perforée ou grille n'est pas collée mais couplée acoustiquement au transducteur par des moyens mécanique de pression.
• La fixation de l'atomiseur sur un support extérieur est réalisée par un clinquant ou un circuit souple fixé par des moyens mécaniques ou par collage sur l'électrode de la céramique qui n'est pas associée au transducteur. Ce mode de fixation particulier est intéressant par sa simplicité de mise en oeuvre et son faible coût. Cette configuration a l'avantage de découpler le transducteur du support extérieur (tenue statique) et de ne pas perturber son fonctionnement dynamique. Par ailleurs, le clinquant métallique (ou le circuit souple) permet d'alimenter électriquement la céramique piézoélectrique.
• L'atomiseur est constitué d'un corps de transducteur qui comprend un moyen de fixation d'un réservoir sans perturber son fonctionnement dynamique et sans altérer ses performances.
• L'atomiseur comprend un réservoir qui est fixé mécaniquement sur le corps du transducteur sans perturber le fonctionnement de celui-ci.
• L'atomiseur comprend un organe mécanique plein ou creux réalisé en différentes matières mais préférentiellement plastique, placé coaxialement à l'intérieur de la cavité contenant le liquide, de forme varié mais préférentiellement cylindrique dont le rôle est de guider les bulles d'air qui pourraient se former au niveau de la membrane vibrante et qui bloqueraient le processus d'atomisation.
• L'atomiseur comprend un capteur de présence de liquide constitué d'une électrode placée à l'intérieur de la « trompe » et proche de la membrane vibrante. On injecte sur cette électrode un courant électrique alternatif basse fréquence dont le signal est récupéré sur la masse électrique du transducteur par traitement. Le courant alternatif se propage de l'électrode à la membrane vibrante via la conductivité du liquide. La présence ou l'absence de ce signal indique la présence ou l'absence de liquide.
• L'atomiseur est placé dans un boîtier de forme varié qui peut se tenir dans la main ou appliqué sur une partie du corps (humain ou animal) comme un masque et réalisé en différentes matières mais préférentiellement en plastique. Ce boîtier peut constituer un diffuseur de parfum, d'humidité, de désinfectant ou de médicament. Tout particulièrement, l'atomiseur associé au boîtier peut être utilisé comme un dispositif de délivrance de médicament par voie pulmonaire, nasale ou oculaire.
• L'atomiseur pourra être associé à un boîtier dédié spécifiquement à la délivrance de médicament par voie pulmonaire. Ce boîtier pourra comporter l'ensemble des fonctions permettant de gérer l'inhalation ou la diffusion de ce médicament. En particulier, il comportera un embout ou un adaptateur anatomique qui peut être jetable, un ensemble de valves ou de chicanes permettant de gérer au mieux le flux d'air (aspiré ou refoulé), un dispositif de déclenchement de l'atomisation à l'inhalation qui peut être réalisé soit mécaniquement soit électroniquement, un réservoir soit à la pression ambiante soit à atmosphère contrôlée (stérile) en dépression, un capteur de niveau de liquide et un mécanisme évitant la formation de bulles d'air tel que décrit dans ce brevet. Dans le présent texte, cet ensemble est désigné comme « inhalateur ».
• L'atomiseur, intégré dans un boîtier mécanique, peut être commandé électroniquement par un boîtier électronique extérieur permettant de l'alimenter par pile, batteries ou secteur. Ce même boîtier électronique peut être intégré dans le boîtier mécanique afin d'assurer une autonomie complète du dispositif. Ce boîtier électronique intégré pourra être alimenté par une batterie, une pile ou un super-condensateur rechargeable soit par le secteur soit par effet inductif.
• L'atomiseur comprend une fonction électronique de détartrage ou plus généralement de débouchage réalisé par un mode d'alimentation électrique particulier en appliquant des cycles de tensions électriques sur l'éléments piézoélectrique de durée, d'amplitude ou de fréquence différents de l'alimentation électronique nominale. Ce mode de débouchage pourra être réalisé alors que l'atomiseur est plongé dans un bain de produit détartrant, nettoyant ou stérilisant.
• L'atomiseur comprend une membrane comportant des trous de taille micronique dont le diamètre a été réduit par le biais d'un traitement de surface (polymère ou métallique) tout particulièrement par dépôt d'or électrolytique. Par ailleurs, ces différents traitements de surface jouent un rôle pour réduire les phénomènes de gouttage ou de bouchage et assurent, dans certains cas, des fonctions bactéricides, virucides ou de biocompatibilité.
• L'atomiseur est constitué de matériaux ou comportant un traitement de surface permettant d'assurer sa stérilisation à froid ou à chaud (étuvage). En particulier, l'atomiseur comprendra des céramiques piézoélectriques haute température (>150°C), un transducteur en acier inoxydable ou en titane, une membrane recouverte d'un flash d'or électrolytique.
• L'atomiseur est connecté électriquement de telle manière que le potentiel électrique de la membrane soit différent de la masse électrique du boîtier électronique. Cette configuration électrique permet de charger électriquement les micro-gouttelettes afin de faciliter le guidage de l'aérosol à travers le circuit aéraulique du dispositif et des voies respiratoires.
• L'atomiseur comprend un mécanisme de perforation réalisé par une canule ou aiguille creuse réalisée, par exemple, en plastique ou en métal placé au centre de l'atomiseur. Ce mécanisme peut comprendre les fonctions d'évitement des bulles d'air et de mesure de niveau de liquide. Ce dispositif de perforation permet de recevoir un réservoir ou un flacon stérile et étanche possédant un opercule de matière élastomère capable d'être perforé.
• L'atomiseur est muni d'un clinquant métallique (ou circuit souple) servant d'électrode et permettant l'alimentation de la céramique qui peut être utilisé pour réaliser un capteur de dépression associé avec la céramique piézoélectrique. La tension générée sur la céramique lors de l'inspiration peut être exploitée pour réaliser un dispositif de déclenchement de l'atomisation à l'inhalation.

Other embodiments of the invention are briefly set out below:

• The piezoelectric element or elements are represented by a single ceramic fixed with a sufficient adhesive rigidity on the transducer subjected to vibratory movement.
• The piezoelectric ceramic is a multilayer allowing a low voltage power supply (1 to 15 V _DC ) as may be provided by, for example, Epcos, Fuji, Noliac, Morgan Matroc or Physic Instruments.
• The piezoelectric ceramic is attached to the transducer body in such a way that there is no contact between the transducer body and the liquid to be atomized. This configuration makes it possible to electrically isolate the piezoelectric ceramic and eliminates any problem of sealing and compatibility (medical application) with the liquid.
• The vibratory motion amplifier (or "horn") of the atomizer has passages, grooves or holes in such a way that the chamber or the liquid reservoir is located around the horn.
• The piezoelectric transducer of the atomizer comprises a "horn" at the end of the "horn" which vibrates preferentially in a "piston" mode without any bending. This "flag" has the advantage of amplifying the vibratory displacement of the transducer but also of being able to fix a micro-perforated membrane of larger diameter. This configuration is intended to increase the flow rate of the atomizer despite its small size.
• The piezoelectric transducer, operating in longitudinal mode, vibrates and deforms a micro-perforated membrane or a cylindrical grid. To optimize the displacement of the cylindrical membrane which is placed between the transducer and the horn, a protrusion can be added in order to rigidify the membrane adequately.
• The atomizer has a "trunk" of particular shape such as, for example, a truncated cone for vibration amplification of movement by abrupt section change. In this particular configuration, the ratio of the membrane-piezoelectric element distance to the diameter of the piezoelectric element is preferably greater than 0.5.
• The micro-perforated membrane or grid is not glued but acoustically coupled to the transducer by mechanical pressure means.
• Fixing the atomizer on an external support is carried out by a foil or a flexible circuit fixed by mechanical means or by bonding to the electrode of the ceramic which is not associated with the transducer. This particular mode of attachment is interesting for its simplicity of implementation and its low cost. This configuration has the advantage of decoupling the transducer from the external support (static behavior) and not to disturb its dynamic operation. Moreover, the metal foil (or the flexible circuit) makes it possible to power the piezoelectric ceramic electrically.
• The atomizer consists of a transducer body which comprises means for fixing a reservoir without disturbing its dynamic operation and without impairing its performance.
• The atomizer comprises a reservoir which is mechanically fixed to the transducer body without disturbing the operation thereof.
• The atomizer comprises a solid or hollow mechanical member made of different materials but preferentially plastic, placed coaxially inside the cavity containing the liquid, of varied but preferably cylindrical shape whose role is to guide the air bubbles that could form at the level of the vibrating membrane and block the atomization process.
• The atomizer comprises a liquid presence sensor consisting of an electrode placed inside the "horn" and close to the vibrating membrane. This electrode is injected with a low frequency alternating electric current whose signal is recovered on the electric mass of the transducer by treatment. AC current is propagated from the electrode to the vibrating membrane via the conductivity of the liquid. The presence or absence of this signal indicates the presence or absence of liquid.
• The atomizer is placed in a case of varied shape that can be held in the hand or applied to a part of the body (human or animal) as a mask and made of different materials but preferably plastic. This housing can be a diffuser of perfume, moisture, disinfectant or medicine. In particular, the atomizer associated with the housing can be used as a pulmonary, nasal or ocular drug delivery device.
• The atomizer may be associated with a dedicated housing specifically for pulmonary drug delivery. This housing may include all the functions to manage the inhalation or diffusion of this drug. In particular, it will include an adapter or an anatomical adapter that can be disposable, a set of valves or baffles to better manage the air flow (sucked or repressed), a device for triggering the atomization to the inhalation which can be achieved either mechanically or electronically, a tank or at ambient pressure or a controlled atmosphere (sterile) vacuum, a liquid level sensor and a mechanism to avoid the formation of air bubbles as described in this patent . In this text, this set is referred to as "inhaler".
• The atomizer, integrated in a mechanical housing, can be controlled electronically by an external electronic box to supply it by battery, batteries or sector. This same electronic box can be integrated in the mechanical housing to ensure a complete autonomy of the device. This integrated electronic box can be powered by a rechargeable battery, battery or super-capacitor either by the sector or by inductive effect.
• The atomizer comprises an electronic descaling function or, more generally, an uncoupling function performed by a particular power supply mode by applying cycles of electrical voltages to the piezoelectric element of different duration, amplitude or frequency of the electronic power supply. nominal. This mode of unblocking can be achieved while the atomizer is immersed in a bath of descaling product, cleaning or sterilizing.
• The atomizer comprises a membrane having micron-sized holes whose diameter has been reduced by means of a surface treatment (polymer or metal), particularly by electrolytic gold deposition. Moreover, these different surface treatments play a role in reducing the phenomena of dripping or clogging and in certain cases ensure bactericidal, virucidal or biocompatible functions.
• The atomizer consists of materials or having a surface treatment to ensure its sterilization cold or hot (steaming). In particular, the atomizer will include high temperature piezoelectric ceramics (> 150 ° C), a stainless steel or titanium transducer, a membrane covered with an electrolytic gold flash.
• The atomizer is electrically connected such that the electrical potential of the membrane is different from the electrical ground of the electronics housing. This electrical configuration makes it possible to electrically charge the micro-droplets in order to facilitate the guidance of the aerosol through the aeraulic circuit of the device and the airways.
• The atomizer comprises a perforation mechanism made by a hollow needle or canula made, for example, of plastic or metal placed in the center of the atomizer. This mechanism may include the functions of air bubble avoidance and liquid level measurement. This perforation device can receive a reservoir or a sterile and sealed bottle having a seal of elastomeric material capable of being perforated.
• The atomizer is provided with a metal foil (or flexible circuit) serving as an electrode and allowing the supply of the ceramic which can be used to produce a vacuum sensor associated with the piezoelectric ceramic. The voltage generated on the ceramic during inspiration can be exploited to produce a device for triggering atomization upon inhalation.

It goes without saying that the invention is not limited to the embodiments described above. These are only examples of others.

It will also be noted that in addition to the introduction of a longitudinal vibration mode, it is possible to provide a radial vibration mode.

Detailed description of the invention

The invention will be better understood in this chapter by means of a detailed description and non-limiting examples illustrated by figures.

Brief description of the figures:

• The figure 1 represents in section an example of atomizer according to the invention.
• The figures 2 , 3, 4, 5 , 6, 7, 8 , 9, 10 and 13 represent in section, variants of this atomizer.
• The figures 11 represent the deformed membranes according to the structure of the atomizers.
• The figures 12 represent models of the vibratory behavior of the atomizer according to the present invention.
• The figure 13 represents a section of an atomizer comprising a tubular vibrating membrane placed around the "horn", itself vibrating in a longitudinal mode.
• The Figures 14 & 15 respectively show perspective views and sections of cylindrical or truncated cone tubular atomizers.
• The figure 16 represents the perspective view and sectional view of a simple T-shaped medical inhaler incorporating an atomizer as described by the present invention.
• The Figures 17A & 17B illustrate two configurations of an inhaler in "pocket" format incorporating an atomizer as described by the present invention. The Figure 17A represents an inhaler controlled by an external electronic box. The Figure 17B represents an inhaler whose electronics are integrated in the housing. The figure 17C shows a section of the same inhaler and shows the position of the atomizer in its case.
• The figure 18 represents the section of an atomizer comprising the various functions of evacuation of air bubbles and of liquid presence sensor.

List of numerical references used in the figures:

1.

Piezoelectric transducer body

1 a.

Stress concentration area

1b.

Zone of amplification of deformations

2.

Monobloc piezoelectric ceramic.

3.

Micro-perforated membrane

4.

Cavity containing the liquid

5.

Rear mass

6.

Prestressing screw.

7.

Electrode.

8.

Link element.

9.

Multilayer piezoelectric ceramic.

10.

Flag

11.

Return of electric mass.

12.

Transducer cover.

13.

Tank.

14.

Plug.

15.

Housing.

16.

Tip.

17.

Openings or valves.

18.

Power cables

19.

Electric case.

20.

Electrical connector.

21.

Coaxial tube.

22.

Liquid presence sensor.

23.

Sensor feedback cable.

The atomizer shown on the Figure 1A comprises a piezoelectric transducer body 1 which is vibrated preferably in the range 50 kHz to 200 kHz. The Figure 1B illustrates the same atomizer but beside which is shown a curve showing the maximum amplitude of the longitudinal displacements of the different parts of the atomizer. The piezoelectric transducer body 1 is characterized by two zones: a stress concentration zone 1a and an amplification zone of the deformations 1b. In the Figures 1 to 6 , the outer diameter of the stress concentration zone 1a is identical to the outer diameter of the deformation amplification zone 1b. However, the internal diameter of the strain amplification zone 1b is greater than the internal diameter of the stress concentration zone 1a.

In the atomizers illustrated on the Figures 7 to 9 the outer diameter of the stress concentration zone 1a is greater than the outer diameter of the deformation amplification zone 1b. On the other hand, the internal diameter of the deformation amplification zone 1b is identical to the internal diameter of the stress concentration zone 1a.

The Figure 8B represents the same type of information that the Figure 1B , ie a curve showing the maximum amplitude of the longitudinal displacements of the different parts of the atomizer.

The inside of the deformation amplification zone 1b consists of a cavity 4 containing the atomizer liquid. In some cases, see in particular the Figures 5.7 and 8 to 10 the cavity 4 extends inside the stress concentration zone 1a. Thanks to this configuration, the ultrasonic energy is mainly preserved in the strain amplification zone 1b, which constitutes an amplifier of vibratory displacements. The energy conservation in the strain amplification zone 1b involves a conversion of the stresses into deformations.

One or more piezoelectric elements, preferably consisting of a one-piece piezoelectric ceramic 2 or multilayer 9, are arranged in the upper part of the atomizer, at the stress concentration zone 1a. The figure 1 for example represents two monoblock piezoelectric ceramics 2 connected by a central electrode 7, for example brass.

The rear mass 5 (dynamic mass) makes it possible to reduce the deformations behind the piezoelectric ceramics. The prestressing screw 6 makes it possible to mechanically bind the assembly of this stack. This assembly constitutes a piezoelectric transducer which is an electromechanical converter which vibrates in a longitudinal mode. A longitudinal mode is defined by the fact that the transducer deforms along its axis of symmetry by elongation or contraction of its section. The vibratory behavior of this type of transducer is essentially governed by its length so that the ratio of the total length of the transducer to the diameter or width of the piezoelectric ceramic is, preferably, greater than or equal to 1.

The micro-perforated membrane 3 or a thin grid (20 to 200 μm) is mechanically fixed to the end of the piezoelectric transducer body 1 where its vibratory speed is maximum. The attachment of the membrane 3 is such that it is acoustically coupled to the transducer in zone 1b. In a first mode of deformation and by way of example, this transducer deforms and vibrates along its half-wavelength. The Figure 1B shows the evolution of the displacement of the points of the transducer in a section along its axis of symmetry (length).

The figure 2 shows the same atomizer provided with a membrane mechanically and acoustically bonded to the transducer via a connecting element 8 to ensure a high prestress on the membrane. In general, the membrane can be mechanically coupled to the zone amplification by gluing, brazing, crimping or welding. In particular, laser welding can be used.

The figure 3 is a variant of the transducer or the rear mass is eliminated for reasons of simplicity of construction. The transducer is dimensioned in such a way that the displacement at the level of the one-piece piezoelectric ceramic 2 is as small as possible and as large as possible in the amplification zone 1b. The electrode 7 may be constituted by fixing a brass foil for example or by gluing a flexible printed circuit on polyimide.

The figure 4 represents a variant of the invention using a multilayer piezoelectric ceramic 9. The layers have a thickness for example of 20 to 200 microns and the use of such multilayers makes it possible, at lower cost, to reduce the power supply voltage across the terminals. ceramic. This configuration is very interesting for applications requiring battery or battery power.

The figure 5 presents a variant of the invention or the cavity (chamber) containing the liquid 4 through the body of the transducer 1 from one side to the other in its length. In this case, the one-piece piezoelectric ceramic 2 has a hole in its center. This configuration makes it easy to feed the cavity with liquid.

The figure 6 shows another type of liquid supply by making passages, holes or grooves to communicate the cavity filled with liquid 4 with the outside. This configuration allows the liquid reservoir to be placed around the transducer.

In the embodiment of the Figures 7 and 8 , the cavity containing the liquid 4 is tubular for reasons of simplicity of form.

In the configuration of the figure 7 , the ceramic 2 is no longer located at the rear of the body of the transducer 1 but at the level of the displacement amplifier at the front of the stress concentration zone 1a. The one-piece piezoelectric ceramic 2 is thus protected by the body of the transducer 1.

This configuration has the advantage of not having the ceramic 2 in contact with the liquid and not to pose sealing problems with the tank. The section variation of the body of the transducer 1 always makes it possible to amplify the vibratory displacement at the level of the membrane 3.

The figure 9 shows another embodiment where the transducer 1 comprises a horn 10 on which is mechanically and acoustically fixed a micro-perforated membrane 3. The advantage of this configuration is to increase the atomized liquid flow by simple surface effect while now a high vibration amplification level.

The figure 10 illustrates, for example, a truncated cone-shaped geometry of the vibratory motion amplifier 1b. This configuration makes it possible to increase the size of the micro-perforated membrane 3.

The figure 11 Explains the vibratory operation of the micro-perforated membrane 3. In the resulting structures of the prior state (11A, 11B, 11C), the atomizer operates in bending by coupling an annular piezoelectric ceramic with the micro-perforated membrane. When the membrane is flat ( Fig. 11A ), the maximum vibratory displacement (U _x ) is at the center of the membrane and decreases sharply when moving away from it. In this case, the jet is very directive. When the membrane is curved and has a dome ( Fig. 11B and 11C ), this one stiffens the mode of vibration and makes diverge by simple geometrical effect the jet. This is observed regardless of the flexural vibration mode considered. The mode 1 bending being more advantageous from this point of view. In the case of the present invention (11D), the geometry and nature of the membrane does not affect the vibration mode of the atomizer. Indeed, the bending stiffness of the membrane has no influence on the longitudinal deformation of the transducer. To obtain the best result, it is sufficient that the diameter of the dome is very close to that of the transducer so that the membrane simply follows the maximum vibratory displacements at this location. Such a configuration ensures the atomizer a greater efficiency and therefore a lower consumption for an identical atomization rate. In addition, the jet is particularly homogeneous and diffuse.

The Figures 12A and 12B show the computed simulations of finite elements of an atomizer made according to the present invention and given as an example.

In this case, the body of the transducer 1 is made of stainless steel. The interior cavity containing the liquid 4 has a diameter of 6mm and the stress concentration zone 1a, has an outer diameter of 16mm.

The strain amplification zone 1b has an outer diameter of 8 mm. The one-piece piezoelectric ceramic 2 is a PIC 255 (Physic Instruments) ceramic with an inside diameter of 8 mm, an outside diameter of 16 mm and a thickness of 1 mm.

The lengths of the transducer 1 and the strain amplification zone 1b are respectively 16mm and 12mm. The micro-perforated membrane 3 was made of electro-formed nickel provided with 800 holes of 5 .mu.m in diameter. The thickness of the membrane is 50 μm and has an outer diameter of 8 mm. The dome has a height of 0.8mm for a diameter of 5mm. The membrane is fixed on the transducer by gluing. The longitudinal modes concerned respectively have resonance frequencies of 77 kHz and 120 kHz.

In the embodiment according to figure 13 , 1a micro-perforated membrane 3 has a cylindrical or tubular geometry. The membrane is fixed on the one hand on the stress concentration zone 1a and, on the other hand, on the strain amplification zone 1b. In this case, the membrane vibrates in a radial fashion.

The Figures 14 & 15 show examples of embodiments which have given excellent results in terms of droplet size and aerosol flow rate. The Figures 14A and 14B describe in perspective and in section a transducer 1 whose body has been made of stainless steel. The inner cavity containing the liquid 4, has a diameter of 6 mm and the stress concentration zone 1a, a diameter of 16 mm. In this specific configuration, the mechanism for fixing the reservoir is like a rear mass 5 in which a thread has been made. The outer diameter and the length of this rear mass are respectively 10mm and 8mm. The one-piece piezoelectric ceramic 2 is a PIC 255 (Physic Instruments) ceramic with an inside diameter of 8 mm, an outside diameter of 16 mm and a thickness of 1 mm. The strain amplification zone 1b (or "trunk") has an outer diameter of 7mm and a length of 12mm.

The electrode 7 enabling the electrical connection of the one-piece piezoelectric ceramic 2 is a stainless steel foil 30 mm in diameter and 50 μm thick. The diaphragm 3 made of electro-formed nickel comprises 10800 holes of 2 μm for a thickness of 20 μm. The atomizer made it possible to obtain droplets with a size of 2 μm for a flow rate of 0.6 ml / min for an operating frequency of 80 kHz.

The Figures 15A and 15B describe in perspective and in section an atomizer whose transducer body 1 has been made of stainless steel. The inner cavity containing the liquid 4 has a diameter which varies from 6mm to 12mm and the stress concentration zone 1a has a diameter of 20mm. In this specific configuration, the mechanism for fixing the reservoir is like a rear mass 5 in which a thread has been made. The outer diameter and the length of this rear mass are respectively 10mm and 8mm. The one-piece piezoelectric ceramic 2 is a PIC 255 (Physic Instruments) ceramic with an inside diameter of 10 mm, an outside diameter of 20 mm and a thickness of 1 mm. The conically-shaped deformation amplification zone 1b (or "trunk") has an outer diameter that varies from 7mm to 14mm and a length of 9mm.

The electrode 7 enabling the electrical connection of the one-piece piezoelectric ceramic 2 is made of stainless steel 30 mm in diameter and 50 μm thick. The membrane 3 in electro-formed nickel comprises 45 300 holes of 2 microns for a thickness of 20 microns. The atomizer made it possible to obtain droplets with a size of 2 μm for a flow rate of 2.5 ml / min for an operating frequency of 70 kHz.

The Figures 16A and 16B describe an inhaler for delivering drugs by the pulmonary route. This inhaler can be in the form of a mouthpiece 16 associated with a T-shaped housing 15 provided, for example, by Intersurgical in which integrates the atomizer object of the present invention. The atomizer is placed in the housing 15 by means of a transducer cover 12. The reservoir 13 provided with its cap 14 carries the transducer 1. The one-piece piezoelectric ceramic 2 is supplied by the electrode 7 in the form of a foil. The atomizer is powered by cables 18. When the atomizer operates, it generates an aerosol inside the housing 15. The patient inhales the aerosol thus generated, via the mouthpiece 16.

The figures 17 describe another form of inhaler. The Figure 17A represents an inhaler integrating the atomizer object of the present invention or the electronic box 19 is placed outside and is connected to the housing 15 of the inhaler by a cable 18. This inhaler comprises a mouthpiece 16, a reservoir 13 bound At the atomizer and a plug 14. Openings 17 have been made in the housing 15 to manage the air flows and the aerosol produced by the atomizer.

The Figure 17B represents an inhaler or the control unit 19 is integrated in the housing 15 of the "pocket" inhaler.

The figure 17C represents, in section, the inhaler of the Figure 17A . We find the housing 15 made for example of molded plastic, the tip 16 which can be removable and disposable after use, the transducer cover 12 which allows to mount the atomizer in the housing 15 and connect to the control unit 19 via the connector 20 and the cable 18. The atomizer consists of the body of the transducer 1, the one-piece piezoelectric ceramic 2, the vibrating membrane 3, the electrode 7, the mass return 11, the reservoir 13 and the plug 14. The aerosol is generated in the housing cavity 15 and aspirated by the patient through the mouthpiece 16.

The figure 18 is a section of an atomizer provided with a tube for the evacuation of air bubbles and a liquid presence sensor. This atomizer comprises a tubular transducer body 1, a one-piece piezoelectric ceramic 2, a micro-perforated vibrating membrane 3 and a rear mass 5 for fixing the reservoir 13. The one-piece piezoelectric ceramic 2 is supplied by a cable 18 connected with a part of the mass return 11 and the electrode 7. A tube 21, preferably plastic and for example 3mm diameter, is placed in the liquid cavity 4 coaxially. When the liquid flow of the atomizer becomes large, the membrane 3 creates a depression such that air can penetrate inside the cavity containing the liquid 4. The formation of air bubbles at the membrane 3 can block the formation of the aerosol and alters the operation of the atomizer. The tube 21 allows the evacuation of the air bubbles by the action of the capillary forces that it exerts on the air-liquid interface. This same tube 21 comprises at its center an electric conductor wire 23 whose end 22 is in electrical contact directly or indirectly with the liquid. An alternating low frequency electrical signal preferably at 500 Hz is transmitted to the conducting wire 23. The membrane 3 and the body of the transducer 1, not being at the same electrical potential, this results in a current due to the resistivity of the liquid present in the the cavity 4. The existence of this current corresponds to the presence of the liquid. The information from the liquid presence sensor 22 makes it possible to start or stop the operation of the atomizer automatically.

The invention is obviously not limited to the examples discussed above. Likewise, it is not limited to the medical field. The atomizer according to the invention can also be used as an odor and perfume diffuser and / or in the application of cosmetic products. The invention also covers the diffusion of mists of various liquids for local use (humidifiers or lubricators) or liquid handling devices for biotechnologies or reagents.

Claims (21)

1. Ultrasound liquid atomizer comprising:

   - a rigid piezoelectric transducer body (1) having a first end defining an opening and a second end, the inside of the piezoelectric transducer body (1) comprising a cavity for containing a liquid to be atomized and said body (1) further comprising a symmetry axis,

   - a micro-perforated membrane (3) attached to said first end and covering said opening,

   - a piezoelectric member (2, 9) adapted and arranged so as to vibrate the piezoelectric transducer body (1),

   characterized in that the piezoelectric member (2, 9) is located toward said second end in order to vibrate the piezoelectric transducer body (1) in a direction parallel to its symmetry axis.
2. Atomizer according to Claim 1, wherein the section of the piezoelectric transducer body (1) varies over its length.
3. Atomizer according to Claim 2, wherein the section varies discontinuously.
4. Atomizer according to Claim 3, wherein the section varies abruptly at a single point.
5. Atomizer according to Claim 4, wherein the thickness of the walls of the piezoelectric transducer body (1) toward said second end is greater than the thickness of the walls of the piezoelectric transducer body (1) toward the first end.
6. Atomizer according to Claim 5, wherein the piezoelectric transducer body is solid toward said second end.
7. Atomizer according to Claim 5, wherein the piezoelectric transducer body is hollow toward said second end.
8. Atomizer according to one of Claims 2, 3 or 4, wherein the internal diameter of the piezoelectric transducer body (1) is constant.
9. Atomizer according to one of Claims 2, 3 or 4, wherein the internal diameter of the piezoelectric transducer body (1) is variable.
10. Atomizer according to Claim 9, wherein the internal diameter toward said first end is greater than the internal diameter toward said second end.
11. Atomizer according to any one of the preceding claims, wherein the piezoelectric member (2, 9) is located at the rear of the body of the transducer 1 or in front of the stress concentration zone.
12. Atomizer according to Claim 11, comprising a rear mass (5) located against the external face of the piezoelectric member (2, 9).
13. Atomizer according to any one of Claims 1 to 10, wherein the external diameter of the piezoelectric transducer body (1) is constant.
14. Atomizer according to any one of Claims 1 to 10, wherein the external diameter of the piezoelectric transducer body (1) is variable.
15. Atomizer according to Claim 14, wherein the external diameter toward said second end is greater than the external diameter toward said first end.
16. Atomizer according to Claim 15, of which the external face of the piezoelectric transducer body is defined by a first diameter and a second diameter, the transition zone between the two diameters forming an abrupt discontinuity.
17. Atomizer according to Claim 16, wherein the piezoelectric member (2) is positioned in the discontinuity and bears on the portion of the piezoelectric transducer body (1) that includes the second end.
18. Atomizer according to any one of the preceding claims, wherein the ratio between the length and the diameter of said cavity is greater than 0.5.
19. Atomizer according to any one of the preceding claims, wherein the micro-perforated membrane (3) at least partially forms a protuberance making it possible to increase its rigidity.
20. Atomizer according to any one of the preceding claims, wherein the micro-perforated membrane (3) has a thickness between 20 and 200 µm and includes holes of a diameter between 1 µm and 100 µm.
21. Atomizer according to any one of the preceding claims, wherein the piezoelectric member is a multi-layer ceramic (9).

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